Reduced Energy Alcohol Separation Process

ABSTRACT

Recovery of alcohols, in particular ethanol, from a crude ethanol product obtained from the hydrogenation of acetic acid using a reduced energy process. The crude ethanol product may be fed to a distillation column in which a substantial portion of the water is removed with the acetic acid in the residue. The ethanol product is obtained from the distillate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional App. No.61/363,109, filed on Jul. 9, 2010, the entirety of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingalcohols and, in particular, to a reduced energy process for recoveringethanol.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulose materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition whenconversion is incomplete, unreacted acid remains in the crude ethanolproduct, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

The need remains for improving the recovery of ethanol from a crudeproduct obtained by reducing alkanoic acids, such as acetic acid, and/orother carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid from anacetic acid feed stream in a reactor to form a crude ethanol productcomprising ethanol, acetic acid, and water. The process furthercomprises separating at least a portion of the crude ethanol product ina column into a first distillate comprising ethanol and a first residuecomprising acetic acid and water, wherein a substantial portion of thewater in the crude ethanol product that is fed to the column is removedin the first residue and recovering ethanol from the first distillate.

In a second embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid from anacetic acid feed stream in a reactor to form a crude ethanol productcomprising ethanol, acetic acid, and water. The process furthercomprises separating at least a portion of the crude ethanol product ina column into a first distillate comprising ethanol and a first residuecomprising acetic acid and water, wherein the first residue comprises amajority of the acetic acid from the crude ethanol product and from 60to 90 wt. % water; and recovering ethanol from the first distillate.

In a third embodiment, the present invention is directed to a processfor producing ethanol comprising hydrogenating acetic acid from anacetic acid feed stream in a reactor to form a crude ethanol productcomprising ethanol, acetic acid, water, and ethyl acetate. The processfurther comprises one or more separation steps. First, at least aportion of the crude ethanol product is separated in a firstdistillation column into a first distillate comprising ethanol, ethylacetate and water, and a first residue comprising acetic acid and water.Next, at least a portion of the first distillate is separated in asecond distillation column to yield a second residue comprising ethanoland water, and a second distillate comprising ethyl acetate with someethanol and water. Depending on the water concentration in the desiredethanol, the process further comprises removing water from the secondresidue. The process may remove water using a distillation column,adsorption unit, membrane, or a combination thereof.

In a fourth embodiment, the present invention is directed to a processfor producing ethanol comprising one or more separation steps to recoverethanol from a crude ethanol product. First, a crude ethanol productcomprising ethanol, acetic acid, water, and ethyl acetate is provided toa column in which at least a portion of the crude ethanol product isseparated into a first distillate comprising ethanol, ethyl acetate andwater, and a first residue comprising acetic acid and water. Next, atleast a portion of the first distillate is separated in a seconddistillation column to yield a second residue comprising ethanol andwater, and a second distillate comprising ethyl acetate. The processfurther comprises removing water from the second residue. In one aspectto recover ethanol, at least a portion of the second residue isseparated in a third distillation column to yield a third distillatecomprising hydrous and anhydrous ethanol and a third residue comprisingwater. In another aspect to recover ethanol, the process furthercomprises removing water from the second residue using an adsorptionunit to form the ethanol product stream. In yet another aspect torecover ethanol, at least a portion of the second residue is separatewith a membrane into a permeate stream comprising water and a retentatestream comprising ethanol and less water than the at least a portion ofthe second residue.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system thatyields a residue stream comprising water and acetic acid in accordancewith one embodiment of the present invention.

FIG. 2 is a schematic diagram of an ethanol production system forremoving water from the ethanol product column in accordance with oneembodiment of the present invention.

FIG. 3 is a schematic diagram of an ethanol production system includinga distillation column to separate a light distillate in accordance withone embodiment of the present invention.

FIG. 4 is a schematic diagram of an ethanol production system forfurther processing the light distillate of FIG. 3 in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst. Thehydrogenation reaction produces a crude ethanol product that comprisesethanol, water, ethyl acetate, unreacted acetic acid, and otherimpurities. To improve operating efficiencies, the processes of thepresent invention involve separating the crude ethanol product into aresidue stream comprising water and unreacted acetic acid and adistillate stream comprising the ethanol product. Advantageously, thisseparation approach results in reducing energy requirements to recoverethanol from the crude ethanol product.

In recovering ethanol, the processes of the present invention use one ormore distillation columns. Unreacted acetic acid is removed from thecrude ethanol product in the residue stream of the initial (first)column to reduce esterification that would consume the desired ethanolproduct. In preferred embodiments, the residue stream comprises asubstantial portion of the water and the unreacted acetic acid from thecrude ethanol product. In one embodiment, the initial column is operatedso that minor amounts of, preferably no, acetic acid is carried over inthe distillate and minor amounts of, preferably no, ethanol is leakedinto the residue. The substantial portion of the water removed in theresidue may vary depending on the composition of the crude ethanolproduct, which is a result of the acetic acid conversion and selectivityto ethanol. In one embodiment, 30 to 90% of the water in the crudeethanol product is removed in the residue, e.g., from 40 to 88% of thewater or from 50 to 84% of the water. Removing less water in the residuemay increase acetic acid carry over in the distillate. In addition,leaving too much water in the residue may also cause increases inethanol leakage into the residue. Also, depending on the conversion, theenergy requirement may also increase when too much water is left in thedistillate.

Preferably, a majority of the water in the crude ethanol product that isfed to the column may be removed in the first residue, for example, upto about 90% of the water from the crude ethanol product, and morepreferably up to about 75%. In some embodiments, with lower conversionsof acetic acid and/or selectivity, the substantial portion of waterwithdrawn as in the residue may be from 30% to 80%, e.g., from 40% to75%.

In an exemplary embodiment, the energy requirements by the initialcolumn in the process according to the present invention may be lessthan 5.5 MMBtu per ton of refined ethanol, e.g., less than 4.5 MMBtu perton of refined ethanol or less than 3.5 MMBtu per ton of refinedethanol. In some embodiments, the process may operate with higher energyrequirements provided that the total energy requirement is less than theenergy required to remove most of the water from the crude ethanolproduct in the distillate, e.g. more than 65% of the water in the crudeethanol product. Additional energy is required to operate an initialcolumn that removes more water in either the distillate and/or residue.The energy requirements for the initial column may increase rapidly whenthe water concentration in the distillate approaches the azeotropicamount, e.g., from about 4 wt. % to about 7 wt. %. To achieve these lowwater concentrations an increase of the reflux ratio is required andresults in an increase of the energy demands on the column. For example,removing additional water, so that more than 90% of the water is removedin the residue, requires a high reflux ratio of greater than 5:1,greater than 10:1 or greater than 30:1. This may place additional energydemands on the distillation column.

The residue stream may comprise at least 85% of the acetic acid from thecrude ethanol product, e.g., at least 90% and more preferably at leastabout 100%. In terms of ranges, the residue stream preferably comprisesfrom 85% to 100% of the unreacted acetic acid from the crude ethanolproduct, and more preferably from 90% to 100%. In one embodiment,substantially all of the unreacted acetic acid is recovered in theresidue stream. By removing substantially all of the unreacted aceticacid from the crude ethanol product, the process, in some aspects, doesnot require further separation of acetic acid from the ethanol product.In this aspect, the ethanol product may contain some acetic acid, e.g.,trace amounts of acetic acid.

The composition of the residue stream may vary depending on acetic acidconversion, as discussed below, as well as the composition of the crudeethanol product and separation conditions in the first column. Dependingon the composition, the residue stream may be: (i) entirely or partiallyrecycled to the hydrogenation reactor, (ii) separated into acid andwater streams, (iii) treated with a solvent in a weak acid recoveryprocess, (iv) reacted with an alcohol to consume the unreacted aceticacid, or (v) disposed to a waste water treatment facility.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also U.S. Pub. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reaction may also compriseother carboxylic acids and anhydrides, as well as acetaldehyde andacetone. Preferably, a suitable acetic acid feed stream comprises one ormore of the compounds selected from the group consisting of acetic acid,acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof.These other compounds may also be hydrogenated in the processes of thepresent invention. In some embodiments, the presence of carboxylicacids, such as propanoic acid or its anhydride, may be beneficial inproducing propanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 kPato 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 1500 kPa.The reactants may be fed to the reactor at a gas hourly space velocity(GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greaterthan 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms of ranges theGHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Suitable hydrogenationcatalysts include catalysts comprising a first metal and optionally oneor more of a second metal, a third metal or any number of additionalmetals, optionally on a catalyst support. The first and optional secondand third metals may be selected from Group IB, IIB, IIIB, IVB, VB,VIIB, VIIB, VIII transition metals, a lanthanide metal, an actinidemetal or a metal selected from any of Groups IIIA, IVA, VA, and VIA.Preferred metal combinations for some exemplary catalyst compositionsinclude platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, cobalt/tin,silver/palladium, copper/palladium, copper/zinc, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron. Exemplarycatalysts are further described in U.S. Pat. No. 7,608,744 and U.S. Pub.No. 2010/0029995, the entireties of which are incorporated herein byreference. In another embodiment, the catalyst comprises a Co/Mo/Scatalyst of the type described in U.S. Pub. No. 2009/0069609, theentirety of which is incorporated herein by reference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium. More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 to 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃,V₂O₅, MnO₂, CuO, CO₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group 111B metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain N or Pro. The Saint-Gobain Nor Pro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry and apacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Sud Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a molepercentage based on acetic acid in the feed. The conversion may be atleast 10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%,at least 70% or at least 80%. Although catalysts that have highconversions are desirable, such as at least 80% or at least 90%, in someembodiments a low conversion may be acceptable at high selectivity forethanol. It is, of course, well understood that in many cases, it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are present in undetectable amounts. Formation of alkanes maybe low, and ideally less than 2%, less than 1%, or less than 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseunreacted acetic acid, ethanol and water. As used herein, the term“crude ethanol product” refers to any composition comprising from 5 to70 wt. % ethanol and from 5 to 40 wt. % water. Exemplary compositionalranges for the crude ethanol product are provided in Table 1. The“others” identified in Table 1 may include, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 15 to 70  15to 50 25 to 50 Acetic Acid 0 to 90 0 to 50 15 to 70 20 to 70 Water 5 to40 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 0 to 20  1 to 12  3to 10 Acetaldehyde 0 to 10 0 to 3  0.1 to 3   0.2 to 2   Others 0.1 to10   0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product comprises acetic acid in anamount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt. %or less than 5 wt. %. In embodiments having lower amounts of aceticacid, the conversion of acetic acid is preferably greater than 75%,e.g., greater than 85% or greater than 90%. In addition, the selectivityto ethanol may also be preferably high, and is preferably greater than75%, e.g., greater than 85% or greater than 90%.

Ethanol Recovery

Exemplary ethanol recovery systems in accordance with embodiments of thepresent invention are shown in FIGS. 1, 2, 3, and 4. Each hydrogenationsystem 100 provides a suitable hydrogenation reactor and a process forseparating ethanol from the crude reaction mixture according to anembodiment of the invention. System 100 comprises reaction zone 101 andseparation zone 102. Reaction zone 101 comprises reactor 103, hydrogenfeed line 104 and acetic acid feed line 105. Separation zone 102comprises a separator 106 and a distillation column 107.

Hydrogen and acetic acid are fed to a vaporizer 108 via lines 104 and105, respectively, to create a vapor feed stream in line 109 that isdirected to reactor 103. In one embodiment, lines 104 and 105 may becombined and jointly fed to the vaporizer 108. The temperature of thevapor feed stream in line 109 is preferably from 100° C. to 350° C.,e.g., from 120° C. to 310° C. or from 150° C. to 300° C. Any feed thatis not vaporized is removed from vaporizer 108 and may be recycled ordiscarded. In addition, although line 109 is shown as being directed tothe top of reactor 103, line 109 may be directed to the side, upperportion, or bottom of reactor 103. Further modifications and additionalcomponents to reaction zone 101 and separation zone 102 are describedbelow.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used upstream of the reactor toprotect the catalyst from poisons or undesirable impurities contained inthe feed or return/recycle streams. Such guard beds may be employed inthe vapor or liquid streams. Suitable guard bed materials may include,for example, carbon, silica, alumina, ceramic, or resins. In one aspect,the guard bed media is functionalized, e.g., silver functionalized, totrap particular species such as sulfur or halogens. During thehydrogenation process, a crude ethanol product stream is withdrawn,preferably continuously, from reactor 103 via line 110.

The crude ethanol product stream in line 110 may be condensed and fed toa separator 106, which, in turn, provides a vapor stream 111 and aliquid stream 112. Suitable separators 106 include a flasher or aknockout pot. The separator 106 may operate at a temperature from 20° C.to 250° C., e.g., from 30° C. to 225° C. or from 60° C. to 200° C. Thepressure of separator 106 may be from 50 kPa to 2000 kPa, e.g., from 75kPa to 1500 kPa or from 100 to 1000 kPa. Optionally, the crude ethanolproduct in line 110 may pass through one or more membranes to separatehydrogen and/or other non-condensable gases.

The vapor stream 111 exiting separator 106 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101. Asshown, vapor stream 111 is combined with the hydrogen feed 104 andco-fed to vaporizer 108. In some embodiments, the returned vapor stream111 may be compressed before being combined with hydrogen feed 104.

The liquid stream 112 from separator 106 is withdrawn and pumped to theside of distillation column 107, also referred to as an “acid separationcolumn” In one embodiment, the contents of liquid stream 112 aresubstantially similar to the crude ethanol product obtained from thereactor, except that the composition has substantially no hydrogen,carbon dioxide, methane or ethane, which are removed by the separator106. Accordingly, liquid stream 112 may also be referred to as a crudeethanol product. Exemplary components of liquid stream 112 are providedin Table 2. It should be understood that liquid stream 112 may containother components, not listed, such as components derived from the feed.

TABLE 2 COLUMN FEED COMPOSITION (Liquid Stream 112) Conc. (wt. %) Conc.(wt. %) Conc. (wt. %) Ethanol 5 to 70 15 to 70 15 to 50 Acetic Acid <90<50 15 to 70 Water 5 to 40  5 to 30 10 to 30 Ethyl Acetate <30 <20  1 to12 Acetaldehyde <10 <3 0.1 to 3   Acetal 5 to 70 15 to 70 15 to 50Acetone 0 to 90  0 to 50 15 to 70 Other Esters  <5 <0.005 <0.001 OtherEthers  <5 <0.005 <0.001 Other Alcohols  <5 <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout presentspecification are preferably not present and if present may be presentin trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, the liquid stream 112may comprise propanol, e.g., isopropanol and/or n-propanol, in an amountfrom 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from 0.001 to 0.03wt. %. In should be understood that these other components may becarried through in any of the distillate or residue streams describedherein and will not be further described herein, unless indicatedotherwise.

Optionally, crude ethanol product in line 110 or in liquid stream 112may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeacetic acid present in the crude ethanol product to further reduce theamount of acetic acid to be removed. Hydrogenolysis may be used toconvert ethyl acetate in the crude ethanol product to ethanol.

Liquid stream 112 is introduced in the lower part of first column 107,e.g., lower half or lower third. In one embodiment, no entrainers areadded to first column 107. In first column 107, water and unreactedacetic acid, along with any other heavy components, if present, areremoved from liquid stream 112 and are withdrawn, preferablycontinuously, as residue in line 113. First column 107 also forms anoverhead distillate, which is withdrawn in line 114, and which may becondensed and refluxed, for example, at a ratio of from 10:1 to 1:10,e.g., from 3:1 to 1:3 or from 1:2 to 2:1. In one embodiment, operatingwith a reflux ratio of less than 5:1 is preferred.

When column 107 is operated under about 170 kPa, the temperature of theresidue exiting in line 113 preferably is from 90° C. to 130° C., e.g.,from 95° C. to 120° C. or from 100° C. to 115° C. The base of column 107may be maintained at a relatively low temperature to withdraw a residuestream comprising both water and acetic acid, thereby providing anenergy efficiency advantage. The temperature of the distillate exitingin line 114 preferably is from 60° C. to 90° C., e.g., from 65° C. to85° C. or from 70° C. to 80° C. In some embodiments, the pressure offirst column 107 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to475 kPa or from 1 kPa to 375 kPa. Exemplary components of the distillateand residue compositions for first column 107 are provided in Table 3below. It should also be understood that the distillate and residue mayalso contain other components, not listed, such as components derivedfrom the feed. For convenience, the distillate and residue of the firstcolumn may also be referred to as the “first distillate” or “firstresidue.” The distillates or residues of the other columns may also bereferred to with similar numeric modifiers (second, third, etc.) inorder to distinguish them from one another, but such modifiers shouldnot be construed as requiring any particular separation order.

TABLE 3 FIRST COLUMN 107 Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 20 to 90  30 to 85  50 to 85 Water 4 to 38 7 to 32  7to 25 Acetic Acid <1 0.001 to 1    0.01 to 0.5  Ethyl Acetate <60 5 to40  8 to 45 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetal <4.0 <3.0<2.0 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Residue Acetic Acid <901 to 50 2.5 to 40  Water 30 to 100 45 to 90  60 to 90 Ethanol <1 <0.9<0.5

In one embodiment, at high conversions of greater than 90%, acetic acidconcentration in the residue may be less than 3 wt. %, e.g. from 0.5 to3 wt. % or from 1 to 2.9 wt. %. Also, at lower conversions of aceticacid, less than 50%, the water concentration in the residue may be lessthan 30 wt. %, or less than 20 wt. %, while the acetic acidconcentration in the residue may be greater than 40 wt. %, e.g., greaterthan 60 wt. % or greater than 80 wt. %.

Some species, such as acetals, may decompose in column 107 such thatvery low amounts, or even no detectable amounts, of acetals remain inthe distillate or residue. In addition, an equilibrium reaction betweenacetic acid and ethanol or between ethyl acetate and water may occur inthe crude ethanol product after it exits reactor 103. Depending on theconcentration of acetic acid in the crude ethanol product, thisequilibrium may be driven toward formation of ethyl acetate. Thisreaction may be regulated using the residence time and/or temperature ofcrude ethanol product.

Depending on the amount of water and acetic acid contained in theresidue of first column 107, line 113 may be treated in one or more ofthe following processes. The following are exemplary processes forfurther treating first residue and it should be understood that any ofthe following may be used regardless of acetic acid concentration. Whenthe residue comprises a majority of acetic acid, e.g., greater than 70wt. %, the residue may be recycled to the reactor without any separationof the water. In one embodiment, the residue may be separated into anacetic acid stream and a water stream when the residue comprises amajority of acetic acid, e.g., greater than 50 wt. %. Acetic acid mayalso be recovered in some embodiments from first residue having a loweracetic acid concentration. The residue may be separated into the aceticacid and water streams by a distillation column or one or moremembranes. If a membrane or an array of membranes is employed toseparate the acetic acid from the water, the membrane or array ofmembranes may be selected from any suitable acid resistant membrane thatis capable of removing a permeate water stream. The resulting aceticacid stream optionally is returned to reactor 103. The resulting waterstream may be used as an extractive agent or to hydrolyze anester-containing stream in a hydrolysis unit.

In other embodiments, for example where residue in line 113 comprisesless than 50 wt. % acetic acid, possible options include one or more of:(i) returning a portion of the residue to reactor 103, (ii) neutralizingthe acetic acid, (iii) reacting the acetic acid with an alcohol, or (iv)disposing of the residue in a waste water treatment facility. It alsomay be possible to separate a residue comprising less than 50 wt. %acetic acid using a weak acid recovery distillation column to which asolvent (optionally acting as an azeotroping agent) may be added.Exemplary solvents that may be suitable for this purpose include ethylacetate, propyl acetate, isopropyl acetate, butyl acetate, vinylacetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue in line 113 comprises less than10 wt. % acetic acid. Acetic acid may be neutralized with any suitablealkali or alkaline earth metal base, such as sodium hydroxide orpotassium hydroxide. When reacting acetic acid with an alcohol, it ispreferred that the residue comprises less than 50 wt. % acetic acid. Thealcohol may be any suitable alcohol, such as methanol, ethanol,propanol, butanol, or mixtures thereof. The reaction forms an ester thatmay be integrated with other systems, such as carbonylation productionor an ester production process. Preferably, the alcohol comprisesethanol and the resulting ester comprises ethyl acetate. Optionally, theresulting ester may be fed to the hydrogenation reactor.

In some embodiments, when the residue comprises very minor amounts ofacetic acid, e.g., less than 5 wt. %, the residue may be disposed of toa waste water treatment facility without further processing. The organiccontent, e.g., acetic acid content, of the residue beneficially may besuitable to feed microorganisms used in a waste water treatmentfacility.

The distillate in line 114 preferably comprises ethanol and optionallyethyl acetate, acetaldehyde, and water. The final ethanol product may bederived from the distillate in line 114. In one embodiment, the weightratio of water in the residue to the water in the distillate is greaterthan 1:1, e.g., greater than 2:1 or greater than 4:1. In addition, theweight ratio of acetic acid in the residue to acetic acid in thedistillate is optionally greater than 10:1, e.g., greater than 15:1 orgreater than 20:1. Preferably, the distillate in line 114 issubstantially free of acetic acid and may contain, if any, only traceamounts of acetic acid.

Depending on the composition of the distillate in line 114, one or morefurther columns or separation units may be used to recover an ethanolproduct having a reduced water content from the distillate in line 114.In FIG. 2, an additional water separation step is used to removeresidual water from the distillate in line 114. In FIGS. 3 and 4,additional columns are shown, which remove light components, such asethyl acetate and acetaldehyde, and result in a purified final ethanolproduct.

The columns shown in FIGS. 1-4 may comprise any distillation columncapable of performing the desired separation and/or purification. Eachcolumn preferably comprises a tray column having from 1 to 150 trays,e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75 trays.The trays may be sieve trays, fixed valve trays, movable valve trays, orany other suitable design known in the art. In other embodiments, apacked column may be used. For packed columns, structured packing orrandom packing may be employed. The trays or packing may be arranged inone continuous column or they may be arranged in two or more columnssuch that the vapor from the first section enters the second sectionwhile the liquid from the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 3000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

In FIG. 2, the distillate in line 114 comprises ethanol, water, andother organics such as ethyl acetate and/or acetaldehyde. In someembodiments, such distillate compositions may be possible at higherselectivities to ethanol, for example, selectivities of greater than90%, greater than 95% or greater than 97%. The amount of water in thedistillate of line 114 may be closer to the azeotropic amount of water,e.g., at least 4 wt. %, that forms with the ethanol/water azeotrope,preferably less than 20 wt. %, e.g., less than 12 wt. % or less than 7.5wt. %.

Depending on the intended ethanol application, it may be desirable toremove water from the distillate in line 114. In some embodiments,removing substantially all of the water produces an anhydrous ethanolproduct suitable for fuel applications. Water may be removed from thedistillate in line 114 using any of several different separationtechniques. Particularly preferred techniques include the use of adistillation column, one or more membranes, one or more adsorption unitsor a combination thereof.

As shown, the first distillate in line 114 is fed to an ethanol productcolumn 118 for separating the first distillate into an ethanoldistillate in line 119 and a water residue in line 120. The firstdistillate in line 114 may be introduced into the lower part of column118, e.g., lower half or lower third. The ethanol distillate 119 fromthe second column 118 preferably is refluxed, for example, at a refluxratio of from 1:10 to 10:1, e.g., from 1:3 to 3:1 or from 1:2 to 2:1.Water residue in line 120 preferably is removed from the system.

Ethanol product column 118 is preferably a tray column as describedabove and preferably operates at atmospheric pressure or below. Thetemperature of the ethanol distillate exiting in line 119 preferably isfrom 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to95° C. The temperature of the water residue in line 120 preferably isfrom 70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to105° C., when the column is operated at atmospheric pressure.

In one embodiment, the ethanol distillate in line 119 may comprise from75 to 96 wt. % ethanol and less than 12 wt. % water. The organics fromthe distillate in line 119, if any, generally carry over and concentratein the ethanol distillate as shown in Table 5 below. Depending on thedesired ethanol application and on the concentration of organics in theethanol distillate, the resulting ethanol distillate in line 119 may bewithdrawn from the system as the final ethanol product. For some ethanolapplications, it may be desirable to remove residual water from theethanol distillate in line 119. Residual water removal may beaccomplished, for example, using an adsorption unit, membrane, molecularsieves, extractive distillation, or a combination thereof. Suitableadsorption units include pressure swing adsorption units and thermalswing adsorption units.

As shown in FIG. 2, an adsorption unit 121 may remove a water stream 122from ethanol distillate in line 119 thus producing an anhydrous ethanolstream 123 comprising 97 wt. %, 99.5 wt. % or more ethanol. Theadsorption unit 121 may employ a suitable adsorption agent such aszeolite 3A or 4A. In one preferred embodiment, adsorption unit 121 is apressure swing adsorption (PSA) unit that is operated at a temperaturefrom 30° C. to 160° C., e.g., from 80° C. to 140° C., and a pressure offrom 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSA unit maycomprise two to five beds. Adsorption unit 121 may remove at least 90%of the water from the treated portion of the ethanol distillate in line119, and more preferably from 95% to 99.99%. Preferably at least 95% ofthe ethanol from the ethanol distillate in line 119 is recovered byadsorption unit 121 in ethanol stream 123, and more preferably at least99% of the ethanol. Water stream 122 may be combined with any otherwater stream from system 100 and preferably is removed from the system.The water stream may also comprise ethanol, in which case it may bedesirable to feed all or a portion of the water stream back to column118 for further ethanol recovery.

In one aspect, not shown, an adsorption unit, membrane, molecularsieves, extractive distillation, or a combination thereof may replaceethanol product column 118. In this aspect, for example, the distillatein line 114 may be fed directly to adsorption unit 121. Column 118 maybe replaced by one or more of these other separation units, for example,when the distillate in line 114 contains less than about 7 wt. % water,e.g., less than 5 wt. % water.

Although the distillate in line 114 in FIG. 2 primarily comprisesethanol and water, in most embodiments of the present invention thedistillate in line 114 may further comprise ethyl acetate andacetaldehyde. As shown in FIG. 3, a second column 115, also referred toas the “light ends column,” may remove ethyl acetate and acetaldehydefrom distillate in line 114. In this embodiment, column 115 produces alight distillate in line 116 comprising ethyl acetate and acetaldehyde,and an ethanol residue in line 117 comprising ethanol and water.

In FIG. 3, distillate in line 114 is introduced to the second column 115preferably in the top part of column, e.g., top half or top third.Second column 115 may be a tray column or packed column. In oneembodiment, second column 115 is a tray column having from 5 to 70trays, e.g., from 15 to 50 trays or from 20 to 45 trays. As one example,when a 30 tray column is utilized in a column without water extraction,line 114 is introduced preferably at tray 2.

Optionally, the light ends column may be an extractive distillationcolumn Suitable extractive agents may include, for example,dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol,hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethyleneglycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane, chlorinatedparaffins, or a combination thereof. In another aspect, the extractiveagent may be an aqueous stream comprising water. If the extraction agentcomprises water, the water may be obtained from an external source orfrom an internal return/recycle line from one or more of the othercolumns, such as from the residue of third column 118 (discussed below).Generally, the extractive agent is fed above the entry point ofdistillate in line 114. When extractive agents are used, a suitablerecovery system, such as a further distillation column, may be used toremove the extractive agent and recycle the extractive agent.

Although the temperature and pressure of second column 115 may vary,when at about 20 kPa to 70 kPa, the temperature of the second residueexiting in line 117 preferably is from 30° C. to 75° C., e.g., from 35°C. to 70° C. or from 40° C. to 65° C. The temperature of the seconddistillate exiting in line 116 preferably is from 20° C. to 55° C.,e.g., from 25° C. to 50° C. or from 30° C. to 45° C. Second column 115may operate at a reduced pressure, near or at vacuum conditions, tofurther favor separation of ethyl acetate and ethanol. In otherembodiments, the pressure of second column 115 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplarycomponents for the distillate and residue compositions for the secondcolumn 115 are provided in Table 4, below. It should be understood thatthe distillate and residue may also contain other components, notlisted, such as components derived from the feed.

TABLE 4 LIGHT ENDS COLUMN 115 Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Second Distillate Ethyl Acetate 5 to 90 10 to 80 15 to 75 Acetaldehyde<60  1 to 40  1 to 35 Ethanol <45 0.001 to 40   0.01 to 35   Water <200.01 to 10   0.1 to 5   Second Residue Ethanol  40 to 99.5 50 to 95 60to 90 Water <60 0.5 to 50  0.1 to 30  Ethyl Acetate <1 0.001 to 2   0.001 to 0.5  Acetic Acid <0.5 <0.01 0.001 to 0.01 

The weight ratio of ethanol in the second residue to ethanol in thesecond distillate preferably is at least 2:1, e.g., at least 5:1, atleast 8:1, at least 10:1 or at least 15:1. The weight ratio of ethylacetate in the second residue to ethyl acetate in the second distillatepreferably is less than 0.7:1, e.g., less than 0.2:1 or less than 0.1:1.It should be understood that when an extractive agent is used, that thecomposition of the residue would also include the extractive agent.

Ethanol residue 117 may be directed to ethanol product column 118, alsoreferred to as the third column, to remove water (in a third residue)from the ethanol product (in third distillate) as discussed above inFIG. 3. Exemplary compositions for the third distillate 119 and thirdresidue 120 are provided below in Table 5. It should be understood thatthe third distillate and the third residue may also contain othercomponents, not listed, such as components derived from the feed.

TABLE 5 ETHANOL PRODUCT COLUMN 118 Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Third Distillate Ethanol 75 to 96  80 to 96 85 to 96 Water <12 1 to 9 3 to 8 Acetic Acid <1 0.001 to 0.1 0.005 to 0.01  Ethyl Acetate<5 0.001 to 4   0.01 to 3   Third Residue Water  75 to 100   80 to 100 90 to 100 Ethanol <0.8 0.001 to 0.5 0.005 to 0.05  Ethyl Acetate <10.001 to 0.5 0.005 to 0.2  Acetic Acid <2 0.001 to 0.5 0.005 to 0.2 

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the ethanoldistillate in amounts of less 0.1 wt. %, based on the total weight ofthe ethanol distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, not shown, the ethanol productcolumn may also form one or more side draw streams for removingimpurities. The impurities may be purged and/or retained within thesystem 100.

The second distillate in line 116, which comprises ethyl acetate and/oracetaldehyde, preferably is refluxed as shown in FIG. 3, for example, ata reflux ratio of from 1:30 to 30:1, e.g., from 1:5 to 5:1 or from 1:3to 3:1. In one aspect, not shown, the second distillate or a portionthereof may be returned to reactor 103. In some embodiments, it may beadvantageous to return a portion of second distillate to reactor 103.The ethyl acetate and/or acetaldehyde in the second distillate may befurther reacted in hydrogenation reactor 103 or in an secondary reactor.The outflow from the secondary reactor may be fed to reactor 103 toproduce additional ethanol or to a distillation column, such as columns,107, 115, or 118, to recover additional ethanol.

In some embodiments the second distillate in line 116 may also compriseup to 12 wt. % water. If all or a portion of the second distillate isreturned to the reactor, it may be necessary to remove water from line116. The water from the second distillate in line 116 may be removed,for example, by an adsorption unit, one or more membranes, molecularsieves, extractive distillation, or a combination thereof. As shown inFIG. 4, an adsorption unit 124 may be used to remove a water stream 126from second distillate in line 116 thus producing a refined light stream125 preferably comprising less than 1 wt. % water and more preferablyless than 0.5 wt. % water. Adsorption unit 124 may remove up to 99.99%of the water from the second distillate in line 116, and more preferablyfrom 95% to 99.99% of the water from the second distillate. Refinedlight stream 125, or a portion thereof, may be returned to reactor 103.

In one embodiment, the light distillate in line 116 and/or the refinedlight distillate in line 125, or a portion of either or both streams,may be further separated to produce an acetaldehyde-containing streamand an ethyl acetate-containing stream. This may allow a portion ofeither the acetaldehyde-containing stream or ethyl acetate-containingstream to be recycled to reactor 103, while purging the other stream.The purge stream may be valuable as a source of either ethyl acetateand/or acetaldehyde.

As shown in FIG. 4, light distillate in line 116 is fed to acetaldehyderemoval column 128, also referred to as a fourth column, to recoveraldehyde that may be recycled to the reactor 103. In fourth column 128,the second distillate is separated into a fourth distillate, whichcomprises acetaldehyde, in line 127 and a fourth residue, whichcomprises ethyl acetate, in line 129. The fourth distillate preferablyis refluxed at a reflux ratio of from 1:20 to 20:1, e.g., from 1:15 to15:1 or from 1:10 to 10:1, and a portion of the fourth distillate isreturned to the reaction zone 101 via line 127. For example, the fourthdistillate may be combined with the acetic acid feed 105, added to thevaporizer 108, or added directly to the reactor 103. Without being boundby theory, since acetaldehyde may be hydrogenated to form ethanol, therecycling of a stream that contains acetaldehyde to the reaction zoneincreases the yield of ethanol and decreases byproduct and wastegeneration. In another embodiment, the acetaldehyde in line 127 may becollected and utilized, with or without further purification, to makeuseful products including but not limited to n-butanol, 1,3-butanediol,and/or crotonaldehyde and derivatives.

The fourth residue of fourth column 128 may be purged via line 129. Thefourth residue primarily comprises ethyl acetate and ethanol, which maybe suitable for use as a solvent mixture or in the production of esters.In one preferred embodiment, the acetaldehyde is removed from the fourthdistillate 127 in fourth column 128 such that the amount of acetaldehydeis present in the residue of column 128 is less than 0.01 wt. %.

Fourth column 128 is preferably a tray column as described above andpreferably operates above atmospheric pressure. In one embodiment, thepressure is from 120 kPa to 5,000 kPa, e.g., from 200 kPa to 4,500 kPa,or from 400 kPa to 3,000 kPa. In a preferred embodiment, the fourthcolumn 128 operates at a pressure that is higher than the pressure ofthe other columns. The temperature of the fourth distillate exiting inline 127 from fourth column 128 preferably is from 60° C. to 110° C.,e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature ofthe fourth residue exiting in line 129 from fourth column 128 preferablyis from 70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C.to 110° C. Exemplary components of the distillate and residuecompositions for fourth column 128 are provided in Table 6 below. Itshould be understood that the distillate and residue may also containother components, not listed, such as components in the feed.

TABLE 6 FOURTH COLUMN 128 Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Fourth Distillate Acetaldehyde 2 to 80    2 to 50 5 to 40 Ethyl Acetate<90   30 to 80 40 to 75  Ethanol <30 0.001 to 25 0.01 to 20   Water <250.001 to 20 0.01 to 15   Fourth Residue Ethyl Acetate 40 to 100    50 to100 60 to 100 Ethanol <40 0.001 to 30 0 to 15 Water <25 0.001 to 20 2 to15 Acetaldehyde <1  0.001 to 0.5 Not detectable Acetal <3 0.001 to 2 0.01 to 1   

Optionally, all or a portion of fourth distillate in line 127 may behydrolyzed to form acetic acid and ethanol from ethyl acetate. Theresulting hydrolyzed stream from the fourth distillate may compriseacetic acid and ethanol and may be fed to first column 107.Alternatively, all or a portion of the fourth distillate may be fed to ahydrogenolysis reactor to reduce ethyl acetate in forming ethanol. Areduced stream from the fourth distillate may comprise ethanol and maybe fed to second column 115 or to third column 118.

In the embodiment shown in FIG. 4, the final ethanol product produced bythe process of the present invention may be taken from the thirddistillate 119. The ethanol product may be an industrial grade ethanolcomprising from 75 to 96 wt. % ethanol, e.g., from 80 to 96 wt. % orfrom 85 to 96 wt. % ethanol, based on the total weight of the ethanolproduct. Exemplary finished ethanol compositional ranges are providedbelow in Table 7.

TABLE 7 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05<0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit asdiscussed above. In such embodiments, the ethanol concentration of theethanol product may be higher than indicated in Table 7, and preferablyis greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greaterthan 99.5 wt. %. The ethanol product in this aspect preferably comprisesless than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0030002 and 2010/0030001, the entire contents and disclosures ofwhich are hereby incorporated by reference. A zeolite catalyst, forexample, may be employed as the dehydration catalyst. Preferably, thezeolite has a pore diameter of at least about 0.6 nm, and preferredzeolites include dehydration catalysts selected from the groupconsisting of mordenites, ZSM-5, a zeolite X and a zeolite Y. Zeolite Xis described, for example, in U.S. Pat. No. 2,882,244 and zeolite Y inU.S. Pat. No. 3,130,007, the entireties of which are hereby incorporatedherein by reference.

In order that the invention disclosed herein may be more efficientlyunderstood, an example is provided below. It should be understood thatthese examples are for illustrative purposes only and is not to beconstrued as limiting the invention in any manner.

EXAMPLES

The following examples were prepared with ASPEN Plus 7.1 simulationsoftware to test various feed composition and separation systems.

Example 1

A crude ethanol product comprising 56 wt. % ethanol, 38 wt. % water, 2wt. % ethyl acetate, 2 wt. % acetaldehyde, 1 wt. % acetic acid, and 1wt. % other organics was fed at 10 lbs per hour into two distillationcolumns in series. The first distillation column operated with 50 traysat 1 atmospheric pressure. The feed tray was located at 35th tray fromthe top. With reflux stream flow rate being twice of that of thedistillate stream, the first column separated the feed mixture into adistillate and residue with the following compositions shown in Table 8.About 90% of the water from the crude ethanol product was removed in theresidue as observed through ASPEN simulation.

TABLE 8 Component (wt. %) Distillate Residue Ethanol 85 <0.01 Water 8 97Ethyl acetate 3 <0.01 Acetaldehyde 2 <0.01 Acetic acid <0.01 3 Otherorganics 2 <0.01 Temperature 75° C. 110° C. Total flow rate 6.6 lb/hr3.4 lb/hr

The distillate from the first column is further sent to a seconddistillation column with 60 stages. The second column operated at about69 kPa and the feed tray was located at the 25th tray from the top. Thereflux stream flow rate is five times the distillate flow rate. Thecompositions of the distillate and residue streams are shown in Table 9.The ethanol product is recovered from the residue of the second column

TABLE 9 Component (wt. %) Distillate Residue Ethanol 30 90 Water 2 8Ethyl acetate 27 0.08 Acetaldehyde 36 — Acetic acid <0.01 — Otherorganics 5 1.2 Temperature 36° C. 69° C. Total flow rate 0.6 lb/hr 6.0lb/hr

Example 2

A crude ethanol product produced by hydrogenation with high conversionof acetic acid, e.g., from 90%, is separated in a distillation column.The amount of ethanol in the residue for each run was less than 0.01 wt.%, except for Run E. As shown in Table 10, the energy requirements forthe column varied with the amount of water removed in the residue.Energy is based on the MMBtu per ton of ethanol refined in the column.In Run A, most of the water is removed in the distillate, and requires asignificant amount of energy to achieve separation.

Runs B-D show an increase of the water from the crude ethanol removed inthe residue, with a decrease in the energy, was observed through ASPENsimulation.

In Run E, 92% of the water from the crude ethanol is removed as theresidue, which causes the amount of ethanol in the residue to increase.In addition, there is a significant amount of energy required for thisseparation that is greater than Run A. The residue for Run E alsocomprised 39.3 wt. % ethanol and 5.4 wt. % ethyl acetate. This reducedthe efficiency of recovering ethanol.

In Run F, the water concentration in the distillate is close to theazeotropic amount using a large reflux ratio of 5:1 to achieve low waterconcentrations. The energy requirements to reduce the waterconcentration in Run F exceeds the energy requirements for Run A.

TABLE 10 High Conversion of Acetic Acid (90%) Run A Run B Run C Run DRun E Run F Distillate - wt. % Ethanol 36.1 40.6 46.4 50.8 16.5 51.6Water 33.4 25.9 15.6 7.8 8.2 6.3 Ethyl Acetate 28.9 32.5 37.1 40.6 74.141.3 Acetic Acid 1.0 0.4 0.07 0.001 <0.01 <0.01 Temperature  87° C.  87°C.  87° C.  87° C. 84° C.  87° C. Residue - wt. % Water 9.2 61.6 66.872.2 40.8 73.0 Acetic Acid 90.1 48.4 33.1 27.8 14.3 27.0 Ethanol <0.01<0.01 <0.01 <0.01 39.3 <0.01 Temperature 122° C. 121° C. 121° C. 120° C.93° C. 120° C. % of Water in 3% 33% 65% 84% 92% 87% Residue Reflux Ratio2:1 2:1 2:1 2:1 2:1 5:1 Energy 9.2 7.27 5.3 4.15 10.26 7.8 (MMBtu/tonETOH)

Example 3

A crude ethanol product produced by hydrogenation with high conversionof acetic acid, e.g., from 99%, is separated in a distillation column.The amount of ethanol in the residue for each run was less than 0.01 wt.%, except for Run L. As shown in Table 11, the energy requirements forthe column varied with the amount of water removed in the residue.Energy is based on the MMBtu per ton of ethanol refined in the column.In Run G, most of the water is removed in the distillate, and requires asignificant amount of energy to achieve separation.

Runs H-K show an increase of the water from the crude ethanol removed inthe residue, with a decrease in the energy, was observed through ASPENsimulation.

In Run L, 92% of the water from the crude ethanol is removed as theresidue, which causes the amount of ethanol in the residue to increase.Although there was a reduction in energy, the residue for Run L alsocomprised 44.7 wt. % ethanol. This reduced the efficiency of recoveringethanol.

TABLE 11 High Conversion of Acetic Acid (99%) Run G Run H Run I Run JRun K Run L Distillate - wt. % Ethanol 56.9 65.9 70.0 80.6 83 77 Water38 28.2 23.7 12.2 9.6 8.8 Ethyl Acetate 2.0 2.4 2.5 2.1 3 5.7 AceticAcid 0.1 <0.01 <0.01 <0.01 <0.01 <0.01 Temperature  92° C.  91° C.  91°C.  89° C.  89° C. 86° C. Residue - wt. % Water 39.9 93.4 95 96.7 96.954 Acetic Acid 60.1 6.6 5 3.3 3.1 2 Ethanol <0.01 <0.01 <0.01 <0.01<0.01 44.7 Temperature 120° C. 120° C. 120° C. 120° C. 120° C. 99° C. %of Water in 2% 37% 50% 76% 83% 92% Residue Reflux Ratio 2:1 2:1 2:1 2:12:1 2:1 Energy 6.79 5.24 4.67 3.54 3.26 3.41 (MMBtu/ton ETOH)

Example 4

A crude ethanol product produced by hydrogenation with high conversionof acetic acid, e.g., from 50%, is separated in a distillation column.The amount of ethanol in the residue for each run was less than 0.01 wt.%, except for Run R. As shown in Table 12, the energy requirements forthe column varied with the amount of water removed in the residue.Energy is based on the MMBtu per ton of ethanol refined in the column.In Run M, most of the water is removed in the distillate, and requires asignificant amount of energy to achieve separation.

Runs N-Q show an increase of the water from the crude ethanol removed inthe residue, with a decrease in the energy, was observed through ASPENsimulation.

In Run R, 92% of the water from the crude ethanol is removed as theresidue, which causes the amount of ethanol in the residue to increase.The residue for Run R also comprised 25.7 wt. % ethanol. This reducedthe efficiency of recovering ethanol.

TABLE 12 Lower Conversion of Acetic Acid (50%) Run M Run N Run O Run PRun Q Run R Distillate - wt. % Ethanol 60.4 67.1 73.6 75.4 76.1 55.9Water 26.6 19.6 12.2 10.1 9.0 7.5 Ethyl Acetate 10.0 11.1 12.2 12.5 12.831.9 Acetic Acid 1.4 0.4 <0.01 <0.01 <0.01 <0.01 Temperature  91° C. 90° C.  89° C.  89° C.  89° C.  85° C. Residue - wt. % Water 1.4 9.415.2 16.6 17.2 15.1 Acetic Acid 98.6 90.6 84.7 83.3 82.0 58.8 Ethanol<0.01 <0.01 <0.01 <0.01 <0.01 25.7 Temperature 126° C. 123° C. 123° C.123° C. 119° C. 109° C. % of Water in 5% 37% 64% 71% 75% 92% ResidueReflux Ratio 2:1 2:1 2:1 2:1 2:1 2:1 Energy 5.61 4.61 3.79 3.59 3.504.63 (MMBtu/ton ETOH)

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

1. A process for producing ethanol, comprising the steps of:hydrogenating acetic acid from an acetic acid feed stream in a reactorto form a crude ethanol product comprising ethanol, acetic acid, andwater; separating at least a portion of the crude ethanol product in acolumn into a first distillate comprising ethanol and a first residuecomprising acetic acid and water, wherein a substantial portion of thewater in the crude ethanol product that is fed to the column is removedin the first residue; and recovering ethanol from the first distillate.2. The process of claim 1, wherein from 30 to 90% of the water in thecrude ethanol product is removed in the first residue stream.
 3. Theprocess of claim 1, wherein at least 50% of the water in the crudeethanol product is removed in the first residue stream.
 4. The processof claim 1, wherein the first residue exits the first distillationcolumn at a temperature from 90° C. to 130° C.
 5. The process of claim1, wherein the first distillate is refluxed at a ratio of less than 5:1.6. The process of claim 1, wherein the first residue comprises from 2.5to 40 wt. % acetic acid, from 60 to 90 wt. % water, and less than 0.5wt. % ethanol.
 7. The process of claim 1, further comprising recoveringacetic acid from the first residue and returning at least a portion ofthe recovered acetic acid to the reactor.
 8. The process of claim 1,wherein the first residue comprises 0 to 10 wt. % acetic acid, theprocess further comprising the step of neutralizing or reacting theacetic acid from the first residue.
 9. The process of claim 1, whereinthe first distillate comprises less than 0.5 wt. % acetic acid.
 10. Theprocess of claim 1, wherein the crude ethanol product further comprisesethyl acetate and acetaldehyde, and the first distillate comprises 50wt. % to 85 wt. % ethanol, 6 wt. % to 17 wt. % water, 8 wt. % to 45 wt.% ethyl acetate, and 0.01 wt. % to 4 wt. % acetaldehyde.
 11. The processof claim 1, further comprising separating at least a portion of thefirst distillate in a second distillation column into a second residuecomprising ethanol and water, and a second distillate comprising ethylacetate.
 12. The process of claim 11, further comprising returning atleast a portion of the second distillate to the reactor.
 13. The processof claim 11, further comprising separating at least a portion of thesecond residue in a third distillation column into a third distillatecomprising ethanol, and a third residue comprising water.
 14. Theprocess of claim 13, wherein the third distillate comprises 75 to 96%ethanol, less than 12 wt. % water, less than 1 wt. % acetic acid, andless than 5% ethyl acetate.
 15. The process of claim 11, furthercomprising reducing the water content of the second residue to yield anethanol product stream with reduced water content.
 16. The process ofclaim 15, wherein the ethanol product stream comprises less than 35 wt.% water.
 17. The process of claim 11, further comprising the steps of:separating at least a portion of the second residue in a thirddistillation column into a third distillate comprising ethanol andwater, and a third residue comprising water; and removing residual waterfrom the third distillate using an adsorption unit to form the ethanolproduct stream.
 18. The process of claim 11, further comprising removingwater from at least a portion of the second residue in an adsorptionunit to yield an ethanol product stream having a lower water contentthan the at least a portion of the second residue.
 19. The process ofclaim 11, further comprising the steps of: separating at least a portionof the second residue in a third distillation column into a thirddistillate comprising ethanol and water, and a third residue comprisingwater; and separating the third distillate with a membrane into apermeate stream comprising water and a retentate stream comprisingethanol and less water than the third distillate.
 20. The process ofclaim 11, further comprising separating at least a portion of the secondresidue with a membrane into a permeate stream comprising water and aretentate stream comprising ethanol and less water than the at least aportion of the second residue.
 21. The process of claim 11, furthercomprising extracting at least a portion of the second residue with oneor more extractive agents to yield an ethanol product stream with areduced water content.
 22. The process of claim 1, further comprisingseparating at least a portion of the first distillate in an ethanolproduct column to yield an ethanol distillate enriched in ethanol and awater residue enriched in water.
 23. The process of claim 1, furthercomprising reducing the water content of the first distillate to yieldan ethanol product stream with reduced water content.
 24. The process ofclaim 23, wherein the ethanol product stream comprises less than 8 wt. %water.
 25. The process of claim 1, further comprising separating atleast a portion of the first distillate in an extractive distillationcolumn with an extractive agent to yield a second residue comprisingethanol, water, and the extractive agent, and a second distillatecomprising ethyl acetate.
 26. The process of claim 1, further comprisingseparating at least a portion the first distillate in a seconddistillation column to yield a second distillate comprising ethylacetate, ethanol, and water, and a second residue comprising ethanol andwater.
 27. The process of claim 26, further comprising removing waterfrom the second distillate using an adsorption unit.
 28. The process ofclaim 26, further comprising separating at least a portion of the seconddistillate with a membrane into a permeate stream comprising water and aretentate stream comprising ethanol, ethyl acetate and less water thanthe at least a portion of the second distillate.
 29. The process ofclaim 1, wherein the first column has an energy requirement of less than5.5. MMBtu per ton of ethanol refined.
 30. The process of claim 1,wherein the acetic acid is formed from methanol and carbon monoxide,wherein each of the methanol, the carbon monoxide, and hydrogen for thehydrogenating step is derived from syngas, and wherein the syngas isderived from a carbon source selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.31. A process for producing ethanol, comprising the steps of:hydrogenating acetic acid from an acetic acid feed stream in a reactorto form a crude ethanol product comprising ethanol, acetic acid, andwater; separating at least a portion of the crude ethanol product in acolumn into a first distillate comprising ethanol and a first residuecomprising acetic acid and water, wherein the first residue comprises amajority of the acetic acid from the crude ethanol product and from 60to 90 wt. % water; and recovering ethanol from the first distillate. 32.The process of claim 31, wherein at least 95% of the acetic acid in thecrude ethanol product is removed in the first residue stream.
 33. Theprocess of claim 31, wherein the first residue comprises from 2.5 to 40wt. % acetic acid, from 60 to 90 wt. % water, and less than 0.5 wt. %ethanol.
 34. A process for producing ethanol, comprising the steps of:hydrogenating acetic acid from an acetic acid feed stream in a reactorto form a crude ethanol product comprising ethanol, acetic acid, water,and ethyl acetate; separating at least a portion of the crude ethanolproduct in a first distillation column into a first distillatecomprising ethanol, ethyl acetate and water, and a first residuecomprising acetic acid and water; separating at least a portion of thefirst distillate in a second distillation column to yield a secondresidue comprising ethanol and water, and a second distillate comprisingethyl acetate; and removing water from the second residue to yieldethanol.
 35. The process of claim 34, further comprising separating atleast a portion of the second residue in a third distillation column toyield a third distillate comprising ethanol and a third residuecomprising water.
 36. The process of claim 34, further comprisingremoving water from the second residue using an adsorption unit to formthe ethanol product stream.
 37. The process of claim 34, furthercomprising separating at least a portion of the second residue with amembrane into a permeate stream comprising water and a retentate streamcomprising ethanol and less water than the at least a portion of thesecond residue.
 38. The process of claim 34, wherein at least 95% of theacetic acid in the crude ethanol product is removed in the first residuestream.
 39. The process of claim 34, wherein at least 50% of the waterin the crude ethanol product is removed in the first residue stream. 40.The process of claim 34, wherein the first residue comprises from 2.5 to40 wt. % acetic acid, from 60 to 90 wt. % water, and less than 0.5 wt. %ethanol.
 41. A process for producing ethanol, comprising the steps of:providing a crude ethanol product comprising ethanol, acetic acid,water, and ethyl acetate; separating at least a portion of the crudeethanol product in a first distillation column into a first distillatecomprising ethanol, ethyl acetate and water, and a first residuecomprising acetic acid and water; separating at least a portion of thefirst distillate in a second distillation column to yield a secondresidue comprising ethanol and water, and a second distillate comprisingethyl acetate; and removing water from the second residue to yieldethanol.